1229976 玖、發明說明： ㈠發明所屬之技術領域 本發明係關於一種無線電通信機之放大電路。 ㈡先前技術 在AM、FM受信機，係將受信信號變換爲中頻信號，再 將中頻信號放大、檢波，最後變換爲聲音信號。中頻信號 之放大電路，如係設計使用雙極電朋體（bi-polar transistor) 時，係把放大器作成複數段之串聯，用以提高放大度，俾 改善/S/N。 在設計使用MOSFET作放大電路時，因MOSFET特有之 問題的1 /f雜訊將增加，故放大器須附加高通濾波器，以 除去Ι/f雜訊。 第3圖爲習用之放大電路，係在串聯連接之放大器間， 插入由電容器與電阻所形成之高通濾波器，用以除去低域 之雜訊。 自前段放大器輸出之信號Vi η，係經過直流阻止用之電 容器C1而輸入至MOSFET 11及12之閘極G°M〇SFET 11、 1 2之閘極上’係賦與由R 1、R2所決定之偏壓電壓，電容 器C2係與電阻R2並聯連接。 MOSFET 1 1及MOSFET 12之汲極D，係分別介由電阻 R3及R4而連接於電源Vd。又，MOSFET 11、12之源極s 係連接於定電流源1 3，此一定電流源1 3之另端則接地。 M0SFET11之汲極，連接由電容器C3與電阻R5所形成 之高通濾波器，電容器C3與電阻R5兩者之連接點，則連 接於MOSFET 13之閘極。又，MOSFET 12之汲極，連接由 1229976 電容器C 4與電阻R 6所形成之高通濾波器，而電容器 與電阻R6兩者之連接點，則連接MOSFET 14之閘極。 MOSFET 13及14之汲極，係分別介由電阻R7及R8 接於電源V d，源極則連接定電流源丨5。 在上述之放大電路中，以MOSFET 11及12所放大之 號，係藉電容器C3與電阻R5所形成之高通濾波器、曁 容器C4與電阻R6所形成之高通濾波器等兩者，將低域 Ι/f雜訊除去。 但是’上述由電容器與電阻所形成之高通濾波器，因 濾波特性之傾向係平穩型，故其濾波之設計，係以通過 的頻率數之信號爲考量，誠難充分除去1 /f雜訊。又， 爲通過特定帶域之信號時，該種放大電路亦難以實現可 去1 /f雜訊及高域之雜訊而具有急峻之濾波特性者。 ㈢發明內容 本發明之課題，係在無線通信機中，可除去1 /f雜訊 高域之雜訊，且可將目的帶域之信號予以放大者。本發 之另一課題，係在放大電路中，可除去1 /f雜訊，並可 目的頻率數之信號放大者。 本發明之放大電路，係具有複數之放大器；及配置於 等複數放大器之後段、可通過特定帶域之信號、以有源 波器所形成之帶通濾波器該等複數之放大器及該帶通 波器兩者，係藉MOS加工處理形成在同一片之積體電路 板上。 倘依本發明，因係使用了以有源濾波器所形成之帶通 波器，故可令濾波器之特性得以急峻化。藉此，即可除 C4 連 信 電 之 其 巨 倘 除 及 明 使 該 濾 濾 基 濾 去 1229976 1 / f雜訊及高域之雜訊，則可將目的帶域之信號予以放大。 本發明之其他放大電路，係具有：複數之放大器；可調 整信號準位之準位調整電路；及配置於該等複數放大器中 之2個以上放大器暨該準位調整電路之後段，可通過藉該 準位調整電路作準位調整後之信號、其特定帶域之信號， 由有源濾波器所形成之帶通濾波器，該複數之放大器、該 準位調整電路、及該帶通濾波器，係藉MOS加工處理予以 形成在同一片積體電路基板上。 倘依本發明，因使用由有源濾波器所形成之帶通濾波 器，故可令濾波器之特性爲急峻化，因而可除去1 /f雜訊 及高域之雜訊，並可放大目的帶域之信號。此外，因可調 整輸入於有源濾波器之信號準位，故可防止有源濾波器之 飽和者。 在本發明，該帶通濾波器爲連接於該複數放大器末段的 放大器輸出。 依此種方式之構成，藉連接於最末段放大器之帶通濾波 器，即可除去在複數放大器所放大之1 /f雜訊。 上述之本發明中，該放大器係限制信號振幅之限幅放大 器而該準位調整電路，係以不使該帶通濾波器飽和、而調 整該限幅放大器之輸出信號的準位，之後輸出於該帶通濾 波器者。 依此種構成，因帶通濾波器不會飽和，故可防止雜訊除 去特性之低下。 本發明之另一種放大電路，係具有複數之放大器；及以 有源濾波器所形成之帶通濾波器，係配置在該複數放大器 1229976 中2個以上放大器之後段’可通過特定頻率數以上之信 號，該等複數放大器及該帶通濾波器係依Μ 0 S加工處理而 形成在同一之積體電路基板上° 倘依本發明，因使用了有源濾波器所形成之帶通濾波 器，故可令濾波之特性急峻化、可除去1 /f雜訊、亦可放 大目的頻率數之信號者。 ㈣實施方式 以下，參照圖面說明本發明之實施例。第1圖爲本發明 實施例之FM/AM受信機用1C中、放大電路及FM檢波電 路之電路圖。此種受信機係以MOS加工處理製造之。 第1圖之電路，係以串聯連接之複數個放大器’將變換 爲中頻信號之FM受信信號放大，又調整信號之準位’而 在帶通濾波器中取出特定帶域之信號之FM檢波電路者。 放大器1 1、1 2、1 3係可限制信號之振幅、並可實行放 大之限幅放大器，並係構成於MOSFET之差動放大電路 中0 準位調整電路1 4，係用以調整放大器1 3之輸出信號的 信號準位，以使帶通濾波器1 5不飽和。 帶通濾波器1 5係由運算放大器、電阻、及電容器構成 爲一種有源濾波器，係一種具有特定之通過帶域特性的濾 波器。帶通濾波器1 5之中心頻率數，例如設計爲1 〇 . 7 Μ Η z 之中頻。又，因係僅用以除去特定頻率數以下之雜訊’故 亦可使用高通濾波器取代該帶通濾波器1 5。 通過帶通濾波器1 5之信號，係在放大器1 6作放大，而 在FM檢波電路1 7中變換爲聲音信號。 1229976 其次，第2圖爲一種將中頻信號放大，於二段限幅放大 器之後，連接以帶通濾波器之放大電路的電路圖。 MOSFET 21及22之汲極D，係介由電阻R21及R22連 接於電源V d，源極S連接於定電流源2 3。 MOSFET 25之閘極G連接於MOSFET 21之汲極D， MOSFET 24之閘極 G則連接於MOSFET 22之汲極 D。 MOSFET 24及25之源極S分別連接定電流源26及27。 上述之MOSFET 24及25係構成射極輸出器電路，把直 流電壓準位予以移位後，即輸出至次段之MOSFET 28及 29 〇 MOSFET 28之閘極G連接於MOSFET 25之源極S， MOSFET 29之閘極G連接於MOSFET 24之源極S。 MOSFET 28之汲極D經電阻R23連接於MOSFET 30之 源極S。MOSFET 30之閘極G連接於汲極D，汲極D連接 於電源Vd。又，MOSFET 28及29之源極S係接於定電流 源31。 MOSFET 24、25、28、29及30等之機能，係用以將輸 入於低通濾波器4 1之信號準位，予以調整爲不使低通濾波 器4 1與高通濾波器42飽和之準位，其等係一種調整電路 者。 MOSFET 28之汲極D，係經電阻R25、R26連接於由 MOSFET之差動放大電路所形成之運算放大器32的非反轉 輸入端子處。又，運算放大器32之非反轉輸入端子亦連接 有電容器C21，電容器C21之另端爲接地。 電阻25及26之連接點處連接有電容器C22，此一電容 1229976 益C 2 2之另一' 纟而係連接運算放大器3 2之輸出。 R27與 端則接 加由電 ΐ 阻 R27 係以使 放大度 、R26、 器41， 率數以 入於由 非反轉 尙連接 阻R3〇 R31及 輸出， 反轉輸 大器33 値，決 運算放大器3 2之反轉輸入端子處，連接有電阻 R 2 8，電阻R 2 7之另端連接於輸出，電阻R 2 8之另 地。亦即，運算放大器3 2之反轉輸入端子處，係施 阻R27與R28將輸出電壓作分壓後之電壓，而以該霄 與R28決定運算放大器32之放大度。又，其設計 電阻R28啓開、電阻27短路，而令運算放大器之 爲” 1 ”之方式爲宜。 由該運算放大器32，電容器C22、C21，電阻R25 R27、R28等所形成之電路4卜係構成一種低通濾波 其以電阻及電容器之値，即可用以決定通過截止頻 下之信號。 運算放大器32之輸出，係經電容器C23、C24輸 MOSFET之差動放大電路所形成之運算放大器33的 輸入端子。又，運算放大器3 3之非反轉輸入端子， 有電阻R29，此一電阻R29之另端爲接地。 電阻R30係接於電容器C23與C24之連接點，電 之另一端係連接於運算放大器3 3之輸出。 運算放大器3 3之反轉輸入端子處，連接有電阻 電阻R32，電阻R31之另端係連接運算放大器33之 電阻R32之另端則接地。亦即，運算放大器33之 入端子處，係施加由電阻R31與電阻R32將運算放： 之輸出電壓作分壓後之電壓，依電阻R31與R32之 定運算放大器33之放大度。 由該運算放大器33、電阻30、電容器C23、C24、電阻 1229976 R 2 9、R 3 1、R 3 3等所構成之電路4 2，係一種高通濾波器4 2， 其係以電阻與電容器之値，決定通過截止頻率數以上之信 號 藉該低通濾器濾4 1與高通波器濾42 ’可通過特定帶域 之信號，因之乃依有源波器濾而構成帶通波器濾。1229976 发明 Description of the invention: ㈠ Technical field to which the invention belongs The present invention relates to an amplifier circuit for a radio communication device. ㈡Previous technology In AM and FM receivers, the received signal is converted into an intermediate frequency signal, and then the intermediate frequency signal is amplified, detected, and finally converted into a sound signal. The IF signal amplifier circuit, if it is designed to use bi-polar transistor (bi-polar transistor), the amplifier is made into a series of complex sections to increase the amplification, 改善 improve / S / N. When designing a MOSFET as an amplifying circuit, the 1 / f noise due to MOSFET-specific problems will increase. Therefore, a high-pass filter must be added to the amplifier to remove the 1 / f noise. Figure 3 is a conventional amplifier circuit. A high-pass filter formed by a capacitor and a resistor is inserted between amplifiers connected in series to remove low-domain noise. The signal Vi η output from the preceding amplifier is input to the gates of the MOSFETs 11 and 12 through the capacitor C1 for DC blocking. G ° MOS, the gates of SFETs 11, 12 are assigned by R 1 and R 2 For the bias voltage, capacitor C2 is connected in parallel with resistor R2. The drain D of the MOSFET 11 and the MOSFET 12 are connected to the power source Vd through resistors R3 and R4, respectively. In addition, the sources s of the MOSFETs 11 and 12 are connected to the constant current source 13, and the other end of the constant current source 13 is grounded. The drain of M0SFET11 is connected to a high-pass filter formed by capacitor C3 and resistor R5. The connection point between capacitor C3 and resistor R5 is connected to the gate of MOSFET 13. The drain of MOSFET 12 is connected to a high-pass filter formed by 1229976 capacitor C 4 and resistor R 6, and the connection point between the capacitor and resistor R 6 is connected to the gate of MOSFET 14. The drains of MOSFETs 13 and 14 are connected to the power supply V d through resistors R7 and R8, respectively, and the source is connected to a constant current source 丨 5. In the above-mentioned amplifying circuit, the numbers amplified by MOSFETs 11 and 12 are the high-pass filter formed by capacitor C3 and resistor R5, and the high-pass filter formed by capacitor C4 and resistor R6. I / f noise is removed. However, the above-mentioned high-pass filter formed by capacitors and resistors is a smooth type because of the tendency of the filtering characteristics. Therefore, the design of the filtering is based on the signals of the passed frequencies. It is difficult to fully remove the 1 / f noise. In addition, in order to pass signals in a specific band, it is difficult for this type of amplifier circuit to achieve 1 / f noise and high-domain noise, and it has sharp filtering characteristics. ㈢ SUMMARY OF THE INVENTION The subject of the present invention is a wireless communication device that can remove noise of 1 / f noise in the high domain and can amplify signals in the target band. Another subject of the present invention is in the amplifier circuit, which can remove 1 / f noise and amplify the signal of the target frequency. The amplifying circuit of the present invention is an amplifier having a complex number; and a plurality of amplifiers and the band pass, which are arranged at the rear of the equal-number amplifier, can pass a signal in a specific band, a band-pass filter formed by an active wave filter, and the band-pass filter. The two wave devices are formed on the same integrated circuit board by MOS processing. According to the present invention, since a band-pass filter formed by an active filter is used, the characteristics of the filter can be sharpened. In this way, the hugeness of the C4 link can be removed. If the filter base is filtered and the 1229976 1 / f noise and high-range noise are removed, the signal in the destination band can be amplified. The other amplifying circuits of the present invention include: a plurality of amplifiers; a level adjustment circuit capable of adjusting a signal level; and two or more amplifiers arranged in the plurality of amplifiers and a subsequent stage of the level adjustment circuit, which can be borrowed by A signal after the level adjustment circuit performs level adjustment, a signal of a specific band range, a bandpass filter formed by an active filter, the plurality of amplifiers, the level adjustment circuit, and the bandpass filter, It is formed on the same integrated circuit board by MOS processing. According to the present invention, since a band-pass filter formed by an active filter is used, the characteristics of the filter can be sharpened, and 1 / f noise and high-range noise can be removed, and the purpose can be amplified. Band signal. In addition, the level of the signal input to the active filter can be adjusted, which can prevent saturation of the active filter. In the present invention, the band-pass filter is an amplifier output connected to the final stage of the complex amplifier. In this way, the 1 / f noise amplified by the complex amplifier can be removed by the band-pass filter connected to the final amplifier. In the invention described above, the amplifier is a limiting amplifier that limits the signal amplitude and the level adjustment circuit adjusts the level of the output signal of the limiting amplifier without saturating the band-pass filter, and then outputs the The band-pass filter. With this configuration, since the band-pass filter is not saturated, it is possible to prevent degradation of noise removal characteristics. Another type of amplifying circuit of the present invention is an amplifier having a complex number; and a band-pass filter formed by an active filter is arranged behind the two or more amplifiers in the complex amplifier 1229976. Signal, the complex amplifiers and the band-pass filter are formed on the same integrated circuit substrate according to M 0 S processing. If the band-pass filter formed by using the active filter according to the present invention, Therefore, the characteristics of filtering can be sharpened, 1 / f noise can be removed, and the signal of the target frequency can be amplified. (Embodiment) An embodiment of the present invention will be described below with reference to the drawings. Fig. 1 is a circuit diagram of a 1C intermediate amplifier circuit and an FM detection circuit for an FM / AM receiver according to an embodiment of the present invention. This type of receiver is manufactured by MOS processing. The circuit in Figure 1 uses a series of multiple amplifiers to 'amplify the FM received signal converted to an intermediate frequency signal and adjust the signal level' to take out the FM detection of a signal in a specific band in a band-pass filter. Circuit person. Amplifier 1 1, 1 2, 1 3 are limiting amplifiers that can limit the amplitude of the signal and can be amplified, and are included in the differential amplifier circuit of the MOSFET. 0 Level adjustment circuit 1 4 is used to adjust the amplifier 1 The signal level of the output signal of 3 makes the bandpass filter 15 not saturated. The band-pass filter 15 is an active filter composed of an operational amplifier, a resistor, and a capacitor, and is a filter having specific passband characteristics. The number of center frequencies of the band-pass filter 15 is, for example, designed as an intermediate frequency of 10.7 Μ Η z. In addition, since it is only used to remove noise below a specific frequency number, a high-pass filter may be used instead of the band-pass filter 15. The signal passing through the band-pass filter 15 is amplified by the amplifier 16 and converted into a sound signal by the FM detection circuit 17. 1229976 Second, Figure 2 is a circuit diagram of an amplifier circuit that amplifies an intermediate frequency signal and connects it with a band-pass filter after a two-stage limiting amplifier. The drain D of the MOSFETs 21 and 22 is connected to the power source V d through the resistors R21 and R22, and the source S is connected to the constant current source 2 3. The gate G of the MOSFET 25 is connected to the drain D of the MOSFET 21, and the gate G of the MOSFET 24 is connected to the drain D of the MOSFET 22. Sources S of MOSFETs 24 and 25 are connected to constant current sources 26 and 27, respectively. The above-mentioned MOSFETs 24 and 25 constitute an emitter output circuit. After the DC voltage level is shifted, it is output to the secondary MOSFETs 28 and 29. The gate G of the MOSFET 28 is connected to the source S of the MOSFET 25, The gate G of the MOSFET 29 is connected to the source S of the MOSFET 24. The drain D of the MOSFET 28 is connected to the source S of the MOSFET 30 via a resistor R23. The gate G of the MOSFET 30 is connected to the drain D, and the drain D is connected to the power source Vd. The source S of the MOSFETs 28 and 29 is connected to the constant current source 31. The functions of MOSFETs 24, 25, 28, 29, and 30 are used to adjust the level of the signal input to the low-pass filter 41, so as not to saturate the low-pass filter 41 and the high-pass filter 42. Bits, etc. are a kind of adjusting circuit. The drain D of the MOSFET 28 is connected to the non-inverting input terminal of the operational amplifier 32 formed by a differential amplifier circuit of the MOSFET via resistors R25 and R26. A capacitor C21 is also connected to the non-inverting input terminal of the operational amplifier 32, and the other end of the capacitor C21 is grounded. A capacitor C22 is connected to the connection point of the resistors 25 and 26. This capacitor 1229976 is another one of C 2 2, and is connected to the output of the operational amplifier 3 2. R27 is connected to the terminal. The resistor R27 is used to increase the magnification, R26, and 41. The rate is calculated by connecting the non-inverting resistor R30R31 and the output. The inverting input amplifier 33 is determined. A resistor R 2 8 is connected to the inverting input terminal of the amplifier 32, the other end of the resistor R 2 7 is connected to the output, and the resistor R 2 8 is connected to another ground. That is, at the inverting input terminal of the operational amplifier 32, the resistors R27 and R28 are used to divide the output voltage into divided voltages, and the amplification of the operational amplifier 32 is determined by the frequency and R28. In addition, its design resistor R28 is turned on and resistor 27 is short-circuited, so that the "1" method of the operational amplifier is suitable. The circuit 4 formed by the operational amplifier 32, capacitors C22, C21, resistors R25, R27, R28, etc. constitutes a kind of low-pass filtering. The combination of resistors and capacitors can be used to determine the signal at the cutoff frequency. The output of the operational amplifier 32 is an input terminal of an operational amplifier 33 formed by a differential amplifier circuit of capacitors C23, C24 and a MOSFET. The non-inverting input terminal of the operational amplifier 33 has a resistor R29, and the other end of this resistor R29 is grounded. The resistor R30 is connected to the connection point of the capacitors C23 and C24, and the other end is connected to the output of the operational amplifier 33. The inverting input terminal of the operational amplifier 33 is connected to a resistor R32, and the other end of the resistor R31 is connected to the other end of the resistor R32 of the operational amplifier 33 to ground. That is, the input terminal of the operational amplifier 33 is applied with the voltage divided by the output voltage of the resistor R31 and the resistor R32, and the amplification of the operational amplifier 33 is determined by the resistors R31 and R32. The circuit 4 2 composed of the operational amplifier 33, resistor 30, capacitors C23, C24, resistor 1229976 R 2 9, R 3 1, R 3 3, etc., is a high-pass filter 4 2 which is composed of a resistor and a capacitor. Alas, it is decided that signals with a cut-off frequency or more can pass through the low-pass filter 41 and high-pass filter 42 'to pass signals in a specific band, so the band-pass filter is formed by active wave filter.
其次，說明以上構成之放大電路的動作。由前段放大器 輸出之信號Vin 1與Vm 2之差壓，係在由MOSFET 21與 MOSFET 22所形成之差動放大器中作放大，在構成爲射極 輸出器電路之MOSFET 24及25中，作電壓移位，而在 MOSFET 28及29之閘極G輸出之。再者，於MOSFET 28 中所放大之信號，係輸出於低通濾波器4 1。 低通濾波器41中，係以電阻R25、R26及電容器C22 之値，決定通過截止頻率數以下之頻率數的信號，較諸截 止頻率數爲高之頻率數的信號，則予衰減之。 又，高通濾波器42中，係以電容器C23、C24，電阻R30 之値，決定通過截止頻率數以上之頻率數的信號，較諸截 止頻率數爲低之頻率數的信號，則予阻止之。該低通濾波 器4 1與該高通濾波器42，係構成帶通濾波器。 此種狀況，令該低通濾波器4 1與該高通濾波器42構成 爲有源濾波器’乃可令濾波器之特性的傾向，達成急峻之 設計。 因之，倘把低通濾波器41之電阻R25，R26,電容器C22 及高通濾波器42之電容器C23，C24，電阻R30等之値作 適當値的設計’即可除去1 /f雜訊及高域之雜訊，且亦可 通過含有目的頻率數之特定帶域的信號。 -12- 1229976 依此，即使在串聯連接之前段放大器放大了 Wf雜訊’ 亦可由配置在後段之帶通濾波器將1 /f雜訊及高域雜訊予 以除去，其輸出之信號即不致含有該等雜訊。 又，因濾波器係由使用MOSFET之有源濾波器所構成’ 故亦可和放大器同樣的，依CMOS加工處理方式形成在 MOS積體電路基板上。 本發明並不限制僅如上述之實施例，其亦可爲以下之構 成： (a) 不僅限制爲 N通道之 MOSFET，亦可爲 P通道 MOSFET、或其他之 MOSFET。 (b) 不僅限制爲FM受信機之限幅放大器，亦可適用於通 信機之其他放大電路。 (c) 帶通濾波器不僅限制如所述及如圖所示之電路，亦 可爲狀態變數型或歸還型之有源濾波器，而運算放大器以 外之差動型有源放大器亦無不可。 倘依本發明，因使用了由有源濾波器所形成之帶通濾波 器，乃可使濾波器之特性急峻化，可除去1 /f雜訊及高域 之雜訊，因而可放大目的帶域之信號。又，因係對有源濾 波器之輸入信號準位作了調整，故亦可防止有源濾波器之 飽和者。 ㈤圖式簡單說明 第丨圖爲本發明實施例之放大電路及FM檢波電路圖。 第2圖爲本發明實施例之放大電路的電路圖。 第3圖爲習用放大電路之電路圖。 符號元件簡單說明 1229976 1 1，1 2, 1 3…放大器 14···準位調整電路 15…帶通濾波器 1 6…放大器 17··· FM檢波電路 2 1，2 2，2 4，2 5，2 8，2 9，3 0…金屬氧化物場效應電晶體 2 3,2 6,27,3 1…定電流源Next, the operation of the amplifier circuit configured as described above will be described. The differential pressure between the signals Vin 1 and Vm 2 output by the preceding amplifier is amplified in a differential amplifier formed by MOSFET 21 and MOSFET 22, and is used as a voltage in MOSFETs 24 and 25 configured as emitter output circuits. Shift, and the gate G of MOSFET 28 and 29 outputs it. Furthermore, the signal amplified in the MOSFET 28 is output to the low-pass filter 41. In the low-pass filter 41, signals that pass frequencies below the cutoff frequency are determined by the resistance of resistors R25, R26, and capacitor C22, and are attenuated compared to signals with higher cutoff frequencies. In addition, the high-pass filter 42 uses the capacitors C23 and C24 and the resistor R30 to determine the signals that pass the frequency above the cutoff frequency, and blocks the signals that have a lower frequency than the cutoff frequencies. The low-pass filter 41 and the high-pass filter 42 constitute a band-pass filter. In such a situation, the low-pass filter 41 and the high-pass filter 42 are configured as active filters', which tends to make the characteristics of the filter and achieve a sharp design. Therefore, if the resistors R25 and R26 of the low-pass filter 41, the capacitor C22 and the capacitors C23 and C24 of the high-pass filter 42 and the resistor R30 are designed appropriately, 1 / f noise and high noise can be removed. Noise in the domain can also pass through signals in a specific band containing the number of frequencies of interest. -12- 1229976 According to this, even if the front stage amplifier amplifies the Wf noise in series connection, the 1 / f noise and high-domain noise can be removed by the band-pass filter configured in the rear stage, and the output signal will not be caused. Contains such noise. In addition, since the filter is composed of an active filter using a MOSFET, it can be formed on a MOS integrated circuit substrate by a CMOS processing method in the same manner as an amplifier. The present invention is not limited to the above-mentioned embodiments, and it can also be configured as follows: (a) It is not limited to N-channel MOSFETs, but also P-channel MOSFETs, or other MOSFETs. (b) Not only limited to the limiting amplifier of the FM receiver, but also applicable to other amplifier circuit of the transmitter. (c) Bandpass filters not only limit the circuits described and shown, but also state-variable or return-type active filters, as well as differential active amplifiers other than operational amplifiers. According to the present invention, since a band-pass filter formed by an active filter is used, the characteristics of the filter can be sharpened, and 1 / f noise and high-domain noise can be removed, so that the target band can be amplified. The signal of the domain. In addition, since the input signal level of the active filter is adjusted, it is also possible to prevent saturation of the active filter. ㈤Brief description of the diagram FIG. 丨 is a diagram of an amplifier circuit and an FM detection circuit according to an embodiment of the present invention. FIG. 2 is a circuit diagram of an amplifier circuit according to an embodiment of the present invention. Figure 3 is a circuit diagram of a conventional amplifier circuit. Brief description of symbol elements 1229976 1 1, 1, 2, 1 3 ... amplifier 14 ... level adjustment circuit 15 ... band pass filter 1 6 ... amplifier 17 ... FM detection circuit 2 1, 2 2, 2 4, 2 5, 2 8, 2 9, 3 0 ... metal oxide field effect transistor 2 3, 2 6, 27, 3 1 ... constant current source
3 2,3 3…運算放大器 41…低通濾波器 42...高通濾波器3 2,3 3 ... Operational amplifier 41 ... Low-pass filter 42 ... High-pass filter
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